A proximity coupler, hereinafter simply referred to as “coupler”, comprises a main transmission line making it possible to route a hyperfrequency signal, and a secondary line of which a section is placed in proximity to the main line. By electromagnetic radiation, the secondary line is thus coupled to the main line. The microstrip technology signal couplers are very widely used because they are inexpensive to make and easy to integrate. However, this technology limits their performance. In particular, a satisfactory coupling directivity, that is to say a good separation of the incoming and outgoing power measurements in the coupler, is difficult to obtain. This difficulty is mainly due to the asymmetries of the even and odd transmission modes that appear with the use of this technology. Finally, in general, the insertion losses and the signal reflections—which are reflected in a non-zero standing wave ratio—are parameters to be taken into account when designing a coupler.
By comparison, the coaxial technology or triplate technology couplers provide for high level performance thanks to the shielding surrounding the propagation lines. However, these technologies increase the bulk and, above all, the fabrication cost of a coupler.
In order to improve the performance level of the microstrip technology couplers toward that of the coaxial or triplate technology couplers, a number of adaptations have already been proposed. Thus, it is known to add one or more capacitive components linking the main transmission line with the coupled secondary line. However, this solution presents a number of drawbacks. On the one hand, components that theoretically have the same capacitive values in reality exhibit capacitance values that are scattered around a mean value. It is therefore difficult to fabricate couplers in series that offer reproducible performance. On the other hand, the implanting of capacitive elements increases the production complexity of the coupler, consequently increasing its fabrication cost. Another known solution is to design transmission lines in singular shapes, in order to optimize the coupling between the main transmission line and the coupled line. However, singularities introduced in the main transmission line often cause the transmission of the signal to be disturbed and therefore the insertion losses to be increased.